saber mini- pulse demo saber (1) mini-pulse demo stss (4 ......new generation of planetary payloads...

Approved for public release; NG 10-1569, 12/8/10.

Small Space Cryocoolers

J. Raab1 and E. Tward

2

Northrop Grumman Aerospace Systems, Redondo Beach, CA, USA 90278

Mechanical long life cryocoolers are an enabling technology used to cool a wide variety of

detectors in space applications. These coolers provide cooling over a range of temperatures from

2K to 200K, cooling powers from tens of mW to tens of watts. Typical applications are missile

warning, Earth and climate sciences, astronomy and cryogenic propellant management. Northrop

Grumman Aerospace Systems (NGAS) has delivered most of the US flight cryocooler systems and

has 16 long life pulse tube coolers on orbit with a cumulative 100 years of continuous orbital

operation with no degradation. This paper will describe these cooler capabilities and the

performance of the 800 gram microcooler.

I. Introduction

The first ever pulse tube cryocooler product was a long life space cooler, the mini space cooler1

designed by

Northrop Grumman Aerospace Systems (NGAS formerly TRW) in the early 1990’s. This mini-pulse tube cooler

was developed as a replacement for Stirling coolers because of producibility and reduced complexity. This followed

3 decades after the pulse tube cooling principle was first described2

and one decade after the first long life space

Stirling cooler was developed3. Since that time these non-wearing space cryocoolers have enabled a number of

space infrared (ir) payloads for earth and atmospheric science, missile defense and long lived astronomical

telescopes. As the specific mass has decreased, the low mass high performance pulse tube cryocoolers can enable a

new generation of planetary payloads not only for ir imaging but also for particles and fields.

All the coolers

made by NGAS are

based on the

principle of the

Oxford Stirling

flexure bearing

technology3 that

results in zero wear

because the flexures

maintain a very stiff

non-contacting gas

bearing between a

moving piston and

cylinder. Following

the launch of a

single miniature

Stirling cooler, all

NGAS cryocoolers

have been pulse tube

coolers that use

Oxford type flexure

bearing moving coil compressors. They differ from the earlier Stirling technology in that the Stirling cooler cold

head containing moving parts with small clearances across a large temperature gradient has been replaced by the

completely passive no moving part pulse tube cold head.

1 Cryocooler Manager, R1/1032, One Space Park, Redondo Beach, CA 90278, and AIAA Regular Member for first

author. 2 Consultant, R1/1032, One Space Park, Redondo Beach, CA 90278. Non-member

Figure 1. NGAS Cooler Flight History and Future

-

'98'98Flight Project Electronics '98 '99 '00 '01 02 '03 '04 '05 '06Cooler '07 '08 '09'97

Airs Class (2)

Hyperion Class (1)

Hyperion Class (2)

OCO (1) Airs Class Airs Class (1)

CX (2) Mini-Pulse

HTSSE (1) Mini Stirling Custom

MTI (1) Airs Class Airs Class (1)

Hyperion (1) Mini-Pulse Hyperion Class (1)

SABER (1) Mini-Pulse Demo

STSS (4) Mini-Pulse Airs Class (4)

AIRS (2) Airs Class Airs Class (2)

TES (2) Airs Class Airs Class (2)

Argos host satellite reached EOL

Launch failure

DemoLewis (2) Mini-Pulse Satellite failure during checkout

GOSAT(1)

JAMI (2)

HEC

HEC

HTP (2) HEC 2 stageGOES ABI HEC 2 stage

HEC 2 stage

MIRI (1) HCC/HEC-JT

NEWT (2) ACE (2)

ACE (2)

ACE

MIRI (1), ACE (1)

-

'98'98Flight Project Electronics '98 '99 '00 '01 02 '03 '04 '05 '06Cooler '07 '08 '09'97

Airs Class

Hyperion Class

Hyperion Class

OCO Airs Class Airs Class

CX Mini- Pulse

HTSSE -2 Mini Stirling Custom

MTI Airs Class Airs Class

HYPERION Mini- Pulse Hyperion Class

SABER Mini- Pulse Demo

STSS Mini- Pulse Airs Class

AIRS Airs Class Airs Class

TES Airs Class Airs Class

Argos host satellite reached EOL

Launch failure

In orbit

DemoLEWIS Mini- Pulse Satellite failure during checkout

Anticipated performance

GOSAT

JAMI

HEC

HEC

HTP HEC 2 stage

GOES ABI HEC 2 stageHEC 2 stage

MIRI HCC/HEC JTNEWT ACE

ACE

ACE

MIRI ,ACE

Future launch

HEC 2 stage

‘10 ‘11

ACE

ACE

ACE

HEC

HEC

‘12

Commercial

OCO-2

NV


Figure 1 shows both the flight history and the planned future flights of NGAS coolers as of December 2010. 16

NGAS vibrationally balanced pulse tube coolers are currently in orbit and all are performing nominally without

failure or changed performance. This represents 16 of the 19 long life United States space flexure bearing Stirling or

pulse tube coolers in orbit and all

the pulse tube coolers in orbit.

Beginning in 1995, NGAS together

with Oxford University developed a

new, very low mass, high

performance compressor whose

mass per unit capacity is

approximately ¼ that of the previous

technology. This design has been

scaled over an order of magnitude in

capacity and size, including the

compressor in the smallest 900 gm

crycooler. Evolution of the

cryocooler drive electronics with

more than 28 flight electronics units

delivered has paralleled that of the

cryocoolers with current generation

electronics in 3 power capacities and

corresponding sizes and the fourth

miniature size under development.

The current generation of coolers

and electronics and their capacities are illustrated in Figure 2 with the cooler capacities and the ultimate low

temperature that can be reached determined by the compressor capacity and the number of cold head temperature

stages. As an example, the high capacity cryocooler (HCC) labeled #1 in Figure 2 has been operated either as a one

stage cooler with 10’s of watt cooling capacity, a 2 stage cooler for cooling large long wave ir focal planes and cold

optics4,5

, a 3 stage 10K cooler for cooling Si:As long wave focal planes and cold optics6 or for zero boiloff cooling

of large space propellant tanks. This same 3 stage cooler will fly as the precooler for a 6K Joule Thomson cooler7

for the James Webb Space Telescope (JWST) Mid Infra Red Instrument (MIRI). The 6K stage Joule Thomson (JT)

driven by the TRL9 HEC compressor/circulator cools the instrument focal plane at a distance of 18 meters from the

precooler. The input power is autonomously controlled by the cooler drive electronics8 to maintain the commanded

temperature while the low self-induced vibration of the vibrationally balanced compressor is further reduced

autonomously with a feedback system.

II. Pulse Tube Micro-cooler

The 900 gram pulse tube micro-cooler9 shown in Figure 3 incorporates a vibrationally balanced compressor

scaled from the TRL 9 HEC10

compressor and a split configuration

coaxial cold head. The space cooler was

designed for dual space and tactical

applications. Its split cold head is

designed either to be bolted to a cold

strap as is typically done for space

coolers or to be integrated into a dewar

in an integrated detector cooler assembly

(IDCA) as is typically done in tactical

instruments. Its 70 gram tactical

electronics is also shown in Figure 3A.

It can be operated in space with the

space qualified 3.8 kg radiation

hardened HEC electronics8 that was

designed for the larger (5x) capacity

Figure 2. NGAS Cryocooler and Electronics Products

Figure 3. Micro-cooler A. With tactical electronics B. Space

configuration

A


HEC cooler or with the smaller 250 gm space electronics now under development. The split mechanical cooler

refrigerates via the cold block, rejecting heat at both the centerplate of the compressor and at the cold head

mounting interface. Inside the

compressor, flexure springs support

the moving-coil linear motor that

synchronously drives the opposed

balanced pistons to minimize the

vibration output. The flexure springs

maintain alignment for the attached

non-contacting pistons. The opposed

pistons oscillate and produce a

sinusoidal pressure wave and a phase

shifted sinusoidal mass flow into the

pulse tube cold head. The very small

clearance between the cylinder and

the piston that seals the compression

space is maintained by the flexure

springs so that the piston and cylinder

never touch. The two vibrationally

balanced opposed compressor halves

operate at the resonant frequency in

the 100Hz range. The pulse tube cold

head is connected via a transfer line

that can be customized for integration into a payload. The coaxial cold head components include the mounting

flange, regenerator, cold block, pulse tube, and their tuning element of inertance and compliant reservoir tank. The

internal wiring in the compressor is designed to have very low outgassing properties after the cooler is baked and

hermetically sealed. All cooler drive power wiring exits the centerplate through a ceramic-insulated hermetic

feedthrough connector designed to maintain the imtenal pressure for decades. Typically a platinum resistance

thermometer (PRT) on the cold block measures the cooling temperature. If required, an accelerometer can be

mounted on the compressor so that together with the signal conditioning electronics, the accelerometer provides a

feedback signal to the vibration control algorithm in the drive electronics.

Current cooler performance for

the space cooler version is shown in

Figure 4. The as tested space cooler

shown in Figure 4 is identical to the

flight configuration shown in Figure

3B except that the reservoir tank end

cap is sealed with a bolted flange

rather than its welded flight

configuration. The tests were

conducted in a thermal vacuum

chamber with varying input powers

and reject temperatures. The

measurements that were taken over a

range of input powers shown by the

data points of Figure 4 are presented

with lines of constant input power

measured between 10W and 49W

and interpolated lines of constant

cooling temperature overlaid over

lines of constant specific power (input power/cooling power). The microcooler cooling capacity at 150K ranges

from 1W to 4.5W as the compressor input power changes from 10W to 49W. Operating the cooler at lower reject

temperature will result in more cooling for the same input power.

The exported vibration signature of the micro cooler without active vibration control has been characterized

with the cooler being driven both with the tactical electronics and by laboratory electronics containing an output

Figure 4. Micro-cooler performance

Figure 5. Micro-cooler self induced vibration along compressor drive

axis

0

5

10

15

20

25

30

35

40

45

50

0 1 2 3 4 5

Co

mp

resso

r In

pu

t P

ow

er

(W)

Cooling Load (W)

300 K Reject

50

8

101216

0

2040

SPECIFIC POWER, W/W

60K 65K

14306080

75K 85K

18100

110K95K

2535

70K 100K80K 90K 120K 130K 140K 150K

45

X


linear drive amplifier. Typical space flight electronics output without additional vibration control is similar to the

linear electronics measurement. Figure 5 shows the typical output vibration along the axis of the moving pistons,

the only moving parts, as measured with force transducers at the mounting surface of the cooler. Note that except for

the facility background noise peaks at 60Hz and below, the vibration output occurs only at the fundamental drive

frequency and its harmonics. The graph shows both the raw data and the actual output after it is corrected for the

facility transfer function for both the tactical electronics and the linear electronics. Even without feedback and the

use of vibration control algorithms in the drive electronics the vibration output is less than 100mN, i.e at levels that

can’t be detected by touch. As shown later for the larger HEC cooler, when feedback to the drive signal is used the

vibration levels can be driven down to below 5mN. The exported vibration along the three axes for the first 5

harmonics of the 95Hz fundamental frequency out to 500Hz are shown in Figure 6 as a function of compressor input

power for the linear drive amplifier case. Note that at all powers the exported vibration is <100mN for all harmonics

in the compressor drive direction.

Figure 6. Micro-cooler self induced vibration as function of input power

III. High Efficency Cooler (HEC): > 35K Single and 2 stage coolers

One and 2 stage versions of the TRL 9 HEC cooler family10

are shown in multiple variants in Figure 7 together

with the matched CCE8. They vary only in the customized cold heads that are optimized for the application. The

compressor and flight electronics are common to all the coolers. They are the most mature of the current NGAS

coolers and have been delivered for flight on 6 programs (Figure 1) and are currently being manufactured for 3 other

programs. HEC coolers are operating in orbit on the Japanese Advanced Meteorological Imager (JAMI) (>5 years to

date) and Greenhouse Gases Observing Satellite/Thermal and near IR sensor for carbon observation

(GOSAT/TANSO) payloads and an additional 17 flight

Figure 7. HEC Single and dual temperature coolers. A: HEC single stage cooler with linear cold head. B: HEC single stage cooler with coaxial cold head. C: HEC 2 stage cooler (ABI cooler) with split coaxial cold head.

D: HEC 2 stage cooler with integral coaxial cold heads. E: Cryocooler control electronics

units (either one or 2 stage) have been delivered. The single stage integral HEC pulse tube cooler with linear

cold head was originally designed to efficiently provide 10W of cooling at 95K as shown in the performance map

(Figure 8A). The flight cooler has also been retuned and delivered to provide cooling at lower temperatures near

40K as shown in Figure 8B. Maximum input power to the HEC mechanical cooler is limited by the maximum

180 W output power of its TRL8 matching drive electronics. Adding a second coaxial cold head that is

pneumatically connected to the HEC compressor through an approximately 0.5 meter transfer line has provided 2

Z

Y

X

0

0.05

0.1

0.15

0.2

0.25

0 10 20 30 40 50

Fo

rce

(N

)

Compressor Input Power (W)

X Direction Force (Drive Axis)Linear Amp, f = 95Hz

f

2f

3f

4f

5f

A

0

0.05

0.1

0.15

0.2

0.25

0 10 20 30 40 50

Fo

rce

(N

)


Y Direction Force (Cross Axis)Linear Amp , f= 95Hz

f

2f

3f

4f

5f

Z

Y

X

B

0

0.05

0.1

0.15

0.2

0.25

0 10 20 30 40 50

Fo

rce

(N

)


Z Direction Force (Vertical Axis)Linear Amp, f = 95 Hz

f

2f

3f

4f

5f

Z

Y

X

C

09-01096_2-006a_154

1st stagecoaxial

cold head

HECcooler

Transfer line

A B C D E


temperature cooling for the Hybrid test Program (HTP) Advanced Baseline Imager (ABI) [Figure 7C] and Newt

payloads as shown in Figure 9.

Figure 8. Performance Map for HEC linear cold head coolers. A: Performance with cold head optimized for

95K. B: Performance with cold head optimized for temperatures below 60K

This split configuration allowed the 1st stage cold head to be located near the device it was cooling. Although the

basic components are the same, operating temperature and loads were accommodated by tuning the two cold heads

with the passive inertance and transfer lines. The thermal performance of the two design variants are shown in

Figures 9A and B.

Figure 9. Performance Map of 2 stage coolers with 2nd stage remote coaxial cold head added to 1 stage HEC

linear cold head cooler. Cooler cold heads were tuned for program loads. A: ABI 2 Stage Cooler performance at

Fixed 124.1W Input Power. B: HTP 2 Stage Cooler performance at fixed 147 W Input Power.

A 3rd

variant of the 2 stage cooler replaces the 2 cold

heads with a pair of integrally mounted coaxial cold heads

in a parallel configuration as shown in Figure 7D. Figure 10

shows the thermal performance map at a fixed 170 W of

input power for this integral two-stage co-axial pulse tube

cooler base on the HEC compressor. This cooler provides

usable cooling down to 35K in a light weight (<6 kg) and

compact size with the flight heritage of the HEC cooler.

Since a real space payload system has a mount with

some unknown compliance we measured the self induced

vibration output at the 2 extreme boundary conditions of 1.

the cooler suspended on bungee cords with the loop closed

around the flight accelerometer and 2. when hard mounted

to a 6 axis dynamometer similar to the measurements of

Figures 5 and 6 . Figure 11A shows the suspended cooler and Figures 11B, 11C, and 11D show the measurements

0

20

40

60

80

100

120

140

160

180

200

0 5 10 15 20 25

Co

mp

resso

r In

pu

t P

ow

er

(W)

Cooling Load (W)

300 K Reject

4

6

8101216

0

204050

SPECIFIC POWER, W/W

55K 60K 67K

14306080

75K 85K

18100

110K120K

95K45K 130K 140K

150K

2535

70K 100K80K 90K

75

80

85

90

95

100

105

110

115

120

125

130

135

140

145

150

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5

Cold Block Load, Watts

Co

mp

resso

r In

pu

t P

ow

er,

Watt

s

50K 55K 60K

80 K

10

12

14

16

1820303540100140

SPECIFIC POWER, W/W

65K 70K 75K

255070

45K40K

120

50

70

90

110

130

150

170

190

30 35 40 45 50 55 60

Integral Cold Head, T, K

Rem

ote C

old

Head

, T

, K

Qintegral = 2.27W

Qremote= 5.24W

Qremote= 0W

Qintegral = 0W

Input Power = 124.1 WattsReject Temperature = 300K

Figure 10. Performance Map for Integral Two-

Stage Coaxial Pulse Tube Cooler

A B

A B


along the three axes when the cooler is hung by bungee cords. Note that the vibration output when controlled by

feedback on the drive axis is below 10mN.

IV. High Cooling Power and Very Low Temperature Coolers

The high cooling power and very low temperature coolers are based on the use of the high capacity compressor

shown as # 1 in Figure 2 and cover a wide range of cooling temperatures from 1.7K to room temperature and

cooling power levels from milliwatts to >100 watts. The 2 stage High Capacity cooler (HCC) is shown in Figure

12A and its coaxial cold head variant is shown in Figure 12B. The coaxial cold head variant was used for the1st two

stages of the 10K cooler shown in Figure 12C and the Mid Infra Red Instrument (MIRI) 6K cooler shown in Figure

12D. Figure 12E shows the large 720W capacity electronics. Not shown is the MIRI 360W capacity electronics.

Typically cryocooler masses are <17kg. The HCC compressor can be driven at powers up to the 720 W capacity of

its electronics if very large cooling powers are required. The HCC cooler of Figure 12A was originally designed to

provide 2 stage cooling nominally at 35 and 85K as configured with its 2 parallel linear cold heads. The cooling

performance at the two stages with input powers up to 600 W are shown in Figure 13A. This cooler is currently in

life test at Air Force Research Laboratory (AFRL). The cooler can be readily retuned to shift load between stages,

either in orbit or for larger range shifts by a minor cold head configuration change after manufacture. The

performance of the coaxial cold head version of this cooler is shown in Figure 13B. Both versions are configured as

A.

B. X-Axis Vibration Output (Pulse Tube Axis)

C. Y-axis Vibration Output (Drive Axis)

D. Z-axis Vibration Output

Figure 11. Cooler Vibration when HEC Cooler is Soft Mounted and loop is closed on flight

accelerometer parallel to Y-Axis. Soft Mounted Cooler is suspended from Bungee cords. It includes a rigid body

water heat exchanger to remove heat while cooler is running.

Y-Axis (Drive Axis)X-Axis (Pulse Tube Axis)

Z-Axis (Vertical Axis)

60 Hz noise


integral coolers to ease payload integration with their single thermal and mechanical interfaces. The HCC cooler can

be controlled and driven by the three variants of the cryocooler control electronics (CCE) that provide maximum

output powers of 180, 360 and 720 W respectively. Choice of drive unit is made to minimize the electronics mass

consistent with the maximum available input power to the electronics from the payload.

Figure 13. High Capacity 2 stage coolers. A. Linear cold head cooler B. Coaxial cold head cooler

The 3-stage 10K pulse tube cooler shown in Figure 12C mounted in a test fixture was designed to provide

cooling at all three stages with the lowest stage operating at 10K. The first stage coaxial configuration cold head is

also used to intercept heat in a parallel 2-stage serial configuration cold head. A performance map of this cooler with

heat loads on the second and third stages is shown in Figure 14A with 300 W input power to the cooler. An

engineering model (EM) version of this cooler was recently integrated into an Infra Red (IR) instrument and cooled

its Si:As focal plane to 11K.

Figure 14. 3 stage Pulse tube cooler A. 10K Cooler Isotherms at 300K Reject and 300 W Input Power B. 6K

cooling of 4 stage hybrid pulse tube/JT cooler at a Distance of 10 meters from cooler

0.5

0.7

0.9

1.1

1.3

1.5

1.7

1.9

2.1

2.3

2.5

0 100 200 300 400 500 600 700

Compressor Input Power, Watts

Co

olin

g L

oad

at 3

5K

, W

atts

0

5

10

15

20

25

Co

olo

ng

Lo

ad

at 8

5K

, W

attsCooling Load at 35K

Cooling Load at 85K

500W Input Power 300K Reject45

50

55

60

65

70

75

80

85

90

24 25 26 27 28 29 30 31 32 33 34 35 36

Stage 2 Temperature (K)

Stag

e 1

Tem

peratu

re (K

)

Stage 1: 82.61 K, 14.27 W Stage 2: 26.78 K, 0 W

Stage 1: 84.98 K, 14.27 WStage 2: 34.98 K, 2.32 W

Stage 1: 52.78 K, 0 WStage 2: 25.15 K, 0 W

Stage 1: 55.53 K, 0 WStage 2: 33.62 K, 2.32 W

0

200

400

600

800

1000

1200

1400

0 100 200 300 400 500

T3 = 8KT3 = 10K

T3 = 15K

T2 = 51K

T2 = 49K

T2 = 47K

Input Power = 300W

Reject = 300K

Co

olin

g L

oad

at S

tag

e 2

, m

W

Cooling Load at Stage3 ,mW

010

20

30

40

50

60

70

80

90

100

110

120

0 100 200 300 400 500

Bus Power (W)

Re

mo

te C

oo

lin

g (m

W)

Figure 12. High capacity and low temperature coolers . A HCC 2 stage cooler. B. HCC coaxial cold head

cooler. C. 3 stage 10K cooler D. MIRI 3 stage precooler with recuperators for lower temperature Joule Thomson

6K stage E. High capacity electronics

D A B C E

A B

A B


The same 3 stage cooler design is used in the MIRI hybrid pulse tube/JT cooler Figure 12D

as a precooler for the gas

flowing in the recuperators of the fourth stage JT cooler. This approach allows the cooler to be on the spacecraft

which is vibrationally isolated from the JWST telescope and instruments located many meters from the spacecraft.

The 6.2K JT cooler stage is powered by a technical readiness level (TRL) 9 HEC single stage compressor and flight

electronics. The measured performance of the MIRI demonstration cooler is shown in Figure 14B. The precooler

also provides shield cooling at 17K at the MIRI instrument.

Conclusion

NGAS coolers cover a wide range of cooling temperatures from 1.7K to room temperature and cooling power

levels from millewatts to 10’s of watts. Widely varying needs are addressed with four basic compressor designs

scaled from the TRL 9 HEC compressor and three cryocooler control electronic designs with power sections scaled

from the TRL 8 180 W advanced cryocooler control electronics. By optimization of the pulse tube cold heads,

adding cooler stages, customizing the mechanical configuration, and a very low temperature JT cooling stage with

remote cooling has allowed this cooler family to address a wide range of requirements. NGAS flight coolers have

demonstrated a total on orbit life of greater than 100 years with no failures or change of performance. Of these units

2 have been in continuous operation for 12 years to date.

References

1. E. Tward, CK Chan, J. Raab, R. Orsini, Miniature Long-Life Space-Qualified Pulse Tube and Stirling

Cryocoolers, Cryocoolers 8: - Plenum Press, 1995

2. Gifford, W.E. and Longsworth, R.C. , Pulse Tube Refrigeration Progress, Advances in Cryogenic Engineering,

Vol. 10, Plenum Press, New York, pp. 69-79

3. G. Davey, Review of the Oxford Cryocooler, Presented at the 1989 Cryogenic Engineering Conference,

University of California Los Angeles, July 1989, Pages 1423-1430.

4. C. Jaco, T. Nguyen, R. Colbert, T. Pietrzak, C.K. Chan and E. Tward, High Capacity Staged Pulse Tube Cooler,

Advances in Cryogenic Engineering (AIP Conference Proceedings), 49B, 1263 (2004).

5. Jaco C., Nguyen T, Tward E. “High Capacity Two-stage Coaxial Pulse Tube Cooler, Adv in Cryogenic

Engineering, Vol. 53A, Amer. Institute of Physics, Melville, NY (2008), pp.530-537.

6. Nguyen, T., R. Colbert, D. Durand, C, Jaco, M. Michaelian, E. Tward , 10K Pulse Tube Cooler, Presented at the

14th International Cryocooler Conference, Annapolis, MD, June 2006, Pages 27-31.

7. D. Durand, D. Adachi, D. Harvey, C. Jaco, M. Michaelian, T. Nguyen, M. Petach, and J. Raab, "Mid InfraRed

Instrument (MIRI) Cooler Subsystem Design," Cryocoolers 15, ICC Press, Boulder, CO (2009), pp 7 - 12.

8. D. Harvey, A. Danial, Thom Davis, J. Godden, M. Jackson, J. McCuskey, P. Valenzuela, Advanced Cryocooler

Electronics for Space , Cryogenics , Volume 44, Issues 6-8 , June-August 2004, Pages 589-593.

9. M. Petach, M. Waterman, E. Tward and P. Bailey, Pulse Tube Microcooler for Space Applications, Presented at

the 14th International Cryocooler Conference, Annapolis, MD, June 2006, Pages 89-93.

10. E. Tward, C. K. Chan, R. Colbert, C. Jaco, , T. Nguyen, R. Orsini, J. Raab , High Efficiency Cryocooler , Adv.

In Cryogenic Engineering, Vol 47B, New York: Amer. Inst. of Physics, 2002, p. 1077.

saber mini- pulse demo saber (1) mini-pulse demo stss (4 ......new generation of planetary payloads...

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